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Message-ID: <CAJfpegtVca6H1JPW00OF-7sCwpomMCo=A2qr5K=9uGKEGjEp3w@mail.gmail.com>
Date: Tue, 12 May 2020 17:04:51 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Mike Kravetz <mike.kravetz@...cle.com>
Cc: syzbot <syzbot+d6ec23007e951dadf3de@...kaller.appspotmail.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Miklos Szeredi <mszeredi@...hat.com>,
syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
Al Viro <viro@...iv.linux.org.uk>
Subject: Re: kernel BUG at mm/hugetlb.c:LINE!
On Tue, Apr 7, 2020 at 12:06 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>
> On 4/5/20 8:06 PM, syzbot wrote:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: 1a323ea5 x86: get rid of 'errret' argument to __get_user_x..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=132e940be00000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=8c1e98458335a7d1
> > dashboard link: https://syzkaller.appspot.com/bug?extid=d6ec23007e951dadf3de
> > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12921933e00000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=172e940be00000
> >
> > The bug was bisected to:
> >
> > commit e950564b97fd0f541b02eb207685d0746f5ecf29
> > Author: Miklos Szeredi <mszeredi@...hat.com>
> > Date: Tue Jul 24 13:01:55 2018 +0000
> >
> > vfs: don't evict uninitialized inode
> >
> > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=115cad33e00000
> > final crash: https://syzkaller.appspot.com/x/report.txt?x=135cad33e00000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=155cad33e00000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+d6ec23007e951dadf3de@...kaller.appspotmail.com
> > Fixes: e950564b97fd ("vfs: don't evict uninitialized inode")
> >
> > overlayfs: upper fs does not support xattr, falling back to index=off and metacopy=off.
> > ------------[ cut here ]------------
> > kernel BUG at mm/hugetlb.c:3416!
> > invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> > CPU: 0 PID: 7036 Comm: syz-executor110 Not tainted 5.6.0-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > RIP: 0010:__unmap_hugepage_range+0xa26/0xbc0 mm/hugetlb.c:3416
> > Code: 00 48 c7 c7 60 37 35 88 e8 57 b4 a2 ff e9 b3 fd ff ff e8 cd 90 c6 ff 0f 0b e9 c4 f7 ff ff e8 c1 90 c6 ff 0f 0b e8 ba 90 c6 ff <0f> 0b e8 b3 90 c6 ff 83 8c 24 c0 00 00 00 01 48 8d bc 24 a0 00 00
> > RSP: 0018:ffffc900017779b0 EFLAGS: 00010293
> > RAX: ffff88808cf5c2c0 RBX: ffffffff8c641c08 RCX: ffffffff81ac50b4
> > RDX: 0000000000000000 RSI: ffffffff81ac58a6 RDI: 0000000000000007
> > RBP: 0000000020000000 R08: ffff88808cf5c2c0 R09: ffffed10129d8111
> > R10: ffffed10129d8110 R11: ffff888094ec0887 R12: 0000000000003000
> > R13: 0000000000000000 R14: 0000000020003000 R15: 0000000000200000
> > FS: 00000000013c0880(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000020000140 CR3: 0000000093554000 CR4: 00000000001406f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> > __unmap_hugepage_range_final+0x30/0x70 mm/hugetlb.c:3507
> > unmap_single_vma+0x238/0x300 mm/memory.c:1296
> > unmap_vmas+0x16f/0x2f0 mm/memory.c:1332
> > exit_mmap+0x2aa/0x510 mm/mmap.c:3126
> > __mmput kernel/fork.c:1082 [inline]
> > mmput+0x168/0x4b0 kernel/fork.c:1103
> > exit_mm kernel/exit.c:477 [inline]
> > do_exit+0xa51/0x2dd0 kernel/exit.c:780
> > do_group_exit+0x125/0x340 kernel/exit.c:891
> > __do_sys_exit_group kernel/exit.c:902 [inline]
> > __se_sys_exit_group kernel/exit.c:900 [inline]
> > __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:900
> > do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> > entry_SYSCALL_64_after_hwframe+0x49/0xb3
>
> This is not new and certainly not caused by commit e950564b97fd.
Sorry for replying late...
> hugetlbf only operates on huge page aligned and sized files/mappings.
> To make sure this happens, the mmap code contians the following to 'round
> up' length to huge page size:
>
> if (!(flags & MAP_ANONYMOUS)) {
> audit_mmap_fd(fd, flags);
> file = fget(fd);
> if (!file)
> return -EBADF;
> if (is_file_hugepages(file))
> len = ALIGN(len, huge_page_size(hstate_file(file)));
> retval = -EINVAL;
> if (unlikely(flags & MAP_HUGETLB && !is_file_hugepages(file)))
> goto out_fput;
> } else if (flags & MAP_HUGETLB) {
> struct user_struct *user = NULL;
> struct hstate *hs;
>
> hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
> if (!hs)
> return -EINVAL;
>
> len = ALIGN(len, huge_page_size(hs));
>
> However, in this syzbot test case the 'file' is in an overlayfs filesystem
> created as follows:
>
> mkdir("./file0", 000) = 0
> mount(NULL, "./file0", "hugetlbfs", MS_MANDLOCK|MS_POSIXACL, NULL) = 0
> chdir("./file0") = 0
> mkdir("./file1", 000) = 0
> mkdir("./bus", 000) = 0
> mkdir("./file0", 000) = 0
> mount("\177ELF\2\1\1", "./bus", "overlay", 0, "lowerdir=./bus,workdir=./file1,u"...) = 0
>
> The routine is_file_hugepages() is just comparing the file ops to huegtlbfs:
>
> if (file->f_op == &hugetlbfs_file_operations)
> return true;
>
> Since the file is in an overlayfs, file->f_op == ovl_file_operations.
> Therefore, length will not be rounded up to huge page size and we create a
> mapping with incorrect size which leads to the BUG.
>
> Because of the code in mmap, the hugetlbfs mmap() routine assumes length is
> rounded to a huge page size. I can easily add a check to hugetlbfs mmap
> to validate length and return -EINVAL. However, I think we really want to
> do the 'round up' earlier in mmap. This is because the man page says:
>
> Huge page (Huge TLB) mappings
> For mappings that employ huge pages, the requirements for the arguments
> of mmap() and munmap() differ somewhat from the requirements for map‐
> pings that use the native system page size.
>
> For mmap(), offset must be a multiple of the underlying huge page size.
> The system automatically aligns length to be a multiple of the underly‐
> ing huge page size.
>
> Since the location for the mapping is chosen BEFORE getting to the hugetlbfs
> mmap routine, we can not wait until then to round up the length. Is there a
> defined way to go from a struct file * to the underlying filesystem so we
> can continue to do the 'round up' in early mmap code?
That's easy enough:
static inline struct file *real_file(struct file *file)
{
return file->f_op != ovl_file_operations ? file : file->private_data;
}
But adding more filesystem specific code to generic code does not
sound like the cleanest way to solve this...
> One other thing I noticed with overlayfs is that it does not contain a
> specific get_unmapped_area file_operations routine. I would expect it to at
> least check for and use the get_unmapped_area of the underlying filesystem?
> Can someone comment if this is by design?
Not sure. What exactly is f_op->get_unmapped_area supposed to do?
> In the case of hugetlbfs, get_unmapped_area is even provided by most
> architectures. So, it seems like we would like/need to be calling the correct
> routine.
Okay.
Thanks,
Miklos
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